Okay. Unscientific at best. I plugged a Wally World 9V into my HF10 for 45 minutes. It got "warm". So, I unplugged it. I let it sit for a while until it was "cool". I then plugged in the AC adapter, 8.4V, for another hour. It got "warm" again. Camera still works.
For the record, probably ~65-70% of the people I asked said, "no problem". The rest said "probably no problem". Here goes nothing...if something breaks, I'll update this thread.
If someone can put my question to rest with absolute authority...please do. Otherwise, off to the races!
--Michael